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Date: Wed, 30 May 2012 14:02:49 -0600
From: Kurt Seifried <kseifried@...hat.com>
To: oss-security@...ts.openwall.com
CC: John Haxby <john.haxby@...cle.com>
Subject: Re: CVE Request -- kernel: tcp: drop SYN+FIN messages

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On 05/30/2012 03:44 AM, John Haxby wrote:
> 
> Recently we have a couple of queries relating to a Nessus "TCP/IP 
> SYN+FIN Packet Filtering Weakness".   This has not been helped by
> the fact that [1] actually points (indrectly) to CVE-2002-2438
> which is actually a SYN+RST problem.
> 
> The Nessus script actually appears to detect this problem (also 
> described in [2]):
> 
> commit fdf5af0daf8019cec2396cdef8fb042d80fe71fa Author: Eric
> Dumazet <eric.dumazet@...il.com> Date:   Fri Dec 2 23:41:42 2011
> +0000
> 
> tcp: drop SYN+FIN messages
> 
> Denys Fedoryshchenko reported that SYN+FIN attacks were bringing
> his linux machines to their limits.
> 
> Dont call conn_request() if the TCP flags includes SYN flag
> 
> Reported-by: Denys Fedoryshchenko <denys@...p.net.lb> 
> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com> Signed-off-by:
> David S. Miller <davem@...emloft.net>
> 
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index
> 78dd38c..0cbb440 100644 --- a/net/ipv4/tcp_input.c +++
> b/net/ipv4/tcp_input.c @@ -5811,6 +5811,8 @@ int
> tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb, goto
> discard;
> 
> if (th->syn) { +            if (th->fin) +                goto
> discard; if (icsk->icsk_af_ops->conn_request(sk, skb) < 0) return
> 1;
> 
> 
> References: [1]
> http://www.nessus.org/plugins/index.php?view=single&id=11618 [2]
> http://markmail.org/thread/l6y5vu3tub434z4w

Please use CVE-2012-2663 for this issue.

This is tracked by Red Hat as:

https://bugzilla.redhat.com/show_bug.cgi?id=826702

- -- 
Kurt Seifried Red Hat Security Response Team (SRT)
PGP: 0x5E267993 A90B F995 7350 148F 66BF 7554 160D 4553 5E26 7993

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